Why does the guard of my sword glow when it shouldn't
Very difficult to say from the description. To track down the cause you can do something like the following :
Remove all the lights and world illumination, does the glow disappear? If not then there must be emission somewhere - hide everything then switch them on one by one in the outliner to narrow down which mesh is causing the problem.
If disabling the lights also disables the glow then the problem is with one of your lights or you have a material that’s effectively amplifying the incident light - disable each material until you find the one causing it and then post details and we can try and point out the cause.